Linear absolute position sensing using capacitive sensing

ABSTRACT

The embodiments described herein are directed to systems and devices for electronically measuring the absolute position of one or more moving targets e.g., along the length of a metal beam using mutual capacitive sensing. The beam may be made of metal and may have a limited inset area to fit a position detection sensor device along its length. The moving targets may have no active elements and the position of multiple targets may be detected simultaneously along the beam. The systems and devices described herein do not utilize electronic position feedback and instead rely on an integrated ruler and minimize the total number of sensors required to support recalibration, thereby minimizing scan time (more sensors results in a linear increase in scan time).

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 63/012,487, filed on Apr. 20, 2021, the disclosure of which ishereby incorporated herein in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to position sensing systems,and more particularly to position sensing systems that utilizecapacitive sensing to determine the position of one or more targets.

BACKGROUND

Capacitive sense arrays function by measuring the capacitance of acapacitive sense element and evaluating for a delta in capacitanceindicating a touch or presence of a conductive object. When a conductiveobject (e.g., a finger, hand, or other object) comes into contact orclose proximity with a capacitive sense element, the capacitance changesand the conductive object is detected. Capacitance sensing systems cansense electrical signals generated on electrodes that reflect changes incapacitance. Such changes in capacitance can indicate a touch event(i.e., the proximity of an object to particular electrodes) and can beused to determine a position/location of the touch event. Thecapacitance changes can be measured by an electrical circuit thatconverts the signals corresponding to measured capacitances of thecapacitive sense elements into digital values. The measured capacitancesare generally received as currents or voltages that are integrated andconverted to the digital values.

There are two typical types of capacitance: 1) mutual capacitance wherethe capacitance-sensing circuit measures a capacitance formed betweentwo electrodes coupled to the capacitance-sensing circuit; 2)self-capacitance where the capacitance-sensing circuit measures acapacitance of a single electrode. Many devices have a distributed loadof capacitance of both types (1) and (2) and some devices sense bothcapacitances either uniquely or in hybrid form with their various sensemodes. Capacitive sense elements are widely used in modern customerapplications (e.g., GPS devices, set-top boxes, cameras, computerscreens, MP3 players, and digital tablets) and can provide reliableoperation under harsh conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

The present embodiments are illustrated by way of example, and not oflimitation, in the figures of the accompanying drawings.

FIG. 1 is a diagram illustrating a position sensing system, according tosome embodiments of the present disclosure.

FIGS. 2A and 2B illustrate a sensor device of the position sensingsystem of FIG. 1 , according to some embodiments of the presentdisclosure.

FIG. 2C illustrates a diagram of Rx signals as a target of the positionsensing system of FIG. 1 moves, according to some embodiments of thepresent disclosure.

FIG. 2D illustrates a table listing the maximum number of uniquecombinations of Rx signals (RX columns) based on a desired positiondetection resolution.

FIGS. 3A-3B illustrate a sensor device of the position sensing system ofFIG. 1 , according to some embodiments of the present disclosure.

FIG. 3C illustrates a diagram of Rx signals as a target of the positionsensing system of FIG. 1 moves, according to some embodiments of thepresent disclosure.

FIG. 4 illustrates a flow diagram of a method for detecting the positionof a target along a beam using capacitive sensing, in accordance withsome embodiments of the present disclosure.

FIG. 5 illustrates an embodiment of a core architecture of theProgrammable System-on-Chip (PSoC®) processing device.

DETAILED DESCRIPTION

In the following description, for purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present embodiments. It will be evident, however,to one skilled in the art that the present embodiments may be practicedwithout these specific details. In other instances, well-known circuits,structures, and techniques are not shown in detail, but rather in ablock diagram in order to avoid unnecessarily obscuring an understandingof this description.

Reference in the description to “one embodiment” or “an embodiment”means that a particular feature, structure, or characteristic describedin connection with the embodiment is included in at least oneembodiment. The phrase “in one embodiment” located in various places inthis description does not necessarily refer to the same embodiment.

Position sensing systems have a wide range of applications includingautomotive, machine tool metrology, disc drive runout measurement, andassembly line testing among others. In the automotive context, manyvehicles are utilizing increasing levels of driver assistance that relyon safety sensors, such as active collision avoidance. Recalibrating thesafety sensors (e.g., lane monitoring cameras, collision detectioncameras) on such vehicles after an accident etc. is becoming morecomplex and critical for safety. For example, various different camerasmay need to be calibrated to make sure they are looking in the rightdirection/at the right area. The position such cameras need to be in maychange from car to car, and manufacturer to manufacturer. Such positionsensing can be difficult, especially in a harsh environment such as anautomotive repair shop. Such position sensing systems may operate bydetecting the position of one or more moving targets (that couldrepresent e.g., various safety sensors) along a fixed track thatincludes position sensors. Electronic position sensors can decreasecalibration errors and allow for the calibrated position to be recordedso that documentation of the calibration process can be provided forlegal compliance.

Currently, there are three methods that are used for non-contactabsolute position detection. The first method is commonly used on rotaryencoders and uses two channels generating sine and cosine signals whichare used to calculate absolute position. This method can be used overlimited linear distances and produces very small signal differences forposition changes over a large length which increases position error.

The second method uses an active sensor on the moving target and apassive sensor pattern on a fixed portion to measure relative position.This method requires active components on the moving target such as apower source and communication hardware, which adds complication andcost to the design. The second method also commonly measures relativeposition movement information and must be calibrated before each use tooutput absolute position. The first two methods described above aresensitive to alignment errors or small levels of contamination that canincrease position error.

The third method uses a linear slider to detect the target locationusing one of two sensor patters. The first pattern is often referred toas a ladder of backgammon pattern and comprises two tapered opposingsensor patterns. Backgammon patterns have poor accuracy as any imbalancein sensor signals creates a position error, and so cannot be used forabsolute position sensing. The second pattern is often referred to as adouble chevron pattern, which comprises a series of discrete sensorpatterns, and can be used to provide absolute position detection.However, the accuracy of such position detection is limited and thetotal number of sensors needed increases linearly with distance. Thus, alarge number of sensors is required along the whole length of the beamwhich in turn results in pin number, routing space, and high parasiticcapacitance constraints. Both sensor patterns have relatively lowaccuracy as they are optimized for human interface where feedback allowsthe user to compensate for target position errors. Additionally, bothsensor methods require periodic target release to update sensor baselinedata to maintain accurate position detection. Periodic target release isgenerally not feasible in mechanical position sensing applications.

The embodiments described herein are directed to systems and devices forelectronically measuring the absolute position of one or more movingtargets e.g., along the length of a metal beam using mutual capacitivesensing. The beam may be made of metal and may have a limited inset areato fit a position detection sensor device along its length. The movingtargets may have no active elements and the position of multiple targetsmay be detected simultaneously along the beam. The systems and devicesdescribed herein do not utilize electronic position feedback and insteadrely on an integrated ruler and minimize the total number of sensorsrequired to support recalibration, thereby minimizing scan time (moresensors results in a linear increase in scan time). The systems anddevices described herein also allow the capacitance of each receiver pinto stay constant relative to the other receiver pins.

In one embodiment, a sensor device is disclosed, the sensor device maycomprise a plurality of receive (Rx) sensors organized into a pluralityof Rx columns, each Rx sensor of the plurality of Rx sensors driven byan Rx signal of a set of Rx signals and wherein the Rx sensors of eachRx column are driven by a unique combination of Rx signals of the set ofRx signals based on a gray code. The sensor device further comprises oneor more transmit (Tx) sensors, each of the one or more transmit sensorsconfigured to capacitively couple to the Rx sensors of one or more Rxcolumns in response to a target moving into proximity of the one or moreRx columns. The sensor device may further comprise a memory and aprocessing device operatively coupled to the memory. The processingdevice may be configured to scan each of the plurality of Rx sensors anddetermine a position of the target based on the scan of each of theplurality of Rx sensors using mutual capacitive sensing.

FIG. 1 illustrates a position sensing system 100 (hereinafter referredto as system 100) in accordance with some embodiments of the presentdisclosure. The system 100 may comprise a measurement beam 105 and oneor more movable optical targets 110A-110D (hereinafter referred to astargets 110). The measurement beam may be of any suitable length (e.g.,750 mm long) and may be made of any appropriate metal. Althoughillustrated as a straight track in FIG. 1 , the measurement beam 105 maycomprise a straight, curved, circular, or any other appropriate shapedtrack. The measurement beam 105 may comprise a channel (not shown) insettherein which provides a limited area within which a sensor device 115may be located along the length of the measurement beam 105. Each target110 may be movably coupled to the measurement beam 105 such that it canmove (e.g., slide) along the measurement beam 105. In some embodiments,instead of being coupled to the measurement beam 105, the targets 110may each be held in alignment with the measurement beam 105 by aseparate mechanical element (e.g., a sliding vice) that may alsofunction to move the targets 110 along the measurement beam 105. Eachtarget 110 may comprise a metal strip that acts as a conductive plate tocapacitively couple the Tx sensors and Rx sensors of the sensor device115 (illustrated in FIGS. 2A and 2B) together as discussed in furtherdetail herein. Each target 110 may have any appropriate width (e.g., 2mm width as shown in FIG. 2A) based on a desired resolution/accuracy ofposition detection. Although illustrated with 4 targets 110, the system100 may comprise any appropriate number of targets 110 as discussed infurther detail herein.

FIG. 2A illustrates a block diagram of the sensor device 115. As shownin FIG. 2A, the sensor device 115 may comprise an Rx sensor pattern 202comprising multiple Rx sensor columns 205A-205L, each with 2 mm spacingas shown in FIG. 2A. Although illustrated in FIG. 2A with 12 Rx sensorcolumns 205, the Rx sensor pattern 202 may comprise any suitable numberof Rx sensor columns 205 with any suitable spacing based on a desiredresolution of position detection, as discussed in further detail herein.It should be noted that the Rx sensor pattern 202 may comprise a totallength of 140 mm, and that the sensor device 115 is illustrated with asingle sensor pattern for ease of illustration and discussion. In orderto cover the entire 750 mm distance of the measurement beam 105, thesensor device 115 may comprise multiple repetitions of the same 140 mmRx sensor pattern 202 until a length of 750 mm is reached. FIG. 2Aillustrates a portion of a first duplicate sensor pattern 202A including3 additional Rx columns as discussed in further detail herein.

Each Rx column 205 may comprise four discrete Rx sensors 206, to form atwo-dimensional matrix (also referred to as an XY matrix) of Rx sensors206. The sensor device 115 may also comprise one or more receive (Rx)channels 207A-207H, and each Rx channel 207A-H may provide a respectiveRx signal (e.g., Rx channel 207A may provide Rx signal 1, Rx channel207B may provide Rx signal 2 etc.) to one or more Rx sensors 206 inorder to measure charge on those Rx sensors 206. In the example of FIG.2A, the sensor device 115 comprises eight Rx channels 207. Each Rxchannel 207 may use any appropriate method for measuring capacitance.Although described with respect to mutual capacitance sensing,embodiments of the present disclosure are not limited in this way andany appropriate method for measuring capacitance may be used. Examplesof such methods may include current versus voltage phase shiftmeasurement, resistor-capacitor charge timing, capacitive bridgedivider, charge transfer, successive approximation, sigma-deltamodulators, charge-accumulation circuits, field effect, mutualcapacitance, and frequency shift, among other capacitance measurementmethods. Each Rx channel 207 may include any appropriate hardware formeasuring capacitance such as a relaxation oscillator (or other means tomeasure capacitance) and a counter or timer to measure the oscillatoroutput. In another example, each Rx channel 207 may include anoperational amplifier, a switch, and an integrator capacitor.

Each Rx sensor 206 may be driven by an Rx signal coming from any of theeight different Rx channels 207. The four Rx sensors 206 each Rx column205 may be driven by a unique combination of four out of the eightpossible Rx signals. The eight Rx signals are routed to the Rx sensors206 with a unique combination for the Rx sensors 206 each Rx column 205using gray code. The equation for the total number of uniquecombinations of Rx signals without repetitions may be given as:Total unique combinations=n!/(r!(n−r)!)where n=number of Rx signals (8) and r=number of Rx sensors per Rxcolumn (4). This gives 70 discrete combinations, thereby allowing fordetection of the position of the target 110A with 2 mm accuracy over the140 mm length of the Rx sensor pattern 202. As shown in FIG. 2A, each Rxsensor 206 includes a number indicating the Rx signal that has beenrouted to it (i.e., is driving it). Each Rx sensor 206 may beelectrically isolated from other Rx sensors 206 having a different inputRx signal. Stated differently, as long as Rx sensors 206 in neighboringRx columns 205 and in the same row represent the same Rx signal, theycan be electrically shorted. This simplifies manufacturing because thesensor pattern may basically comprise long strips that are shortedtogether. Stated differently, because only one Rx sensor 206 changes itsRx signal from column to column, the shorted together rows on Rx sensorswith the same Rx signal act as routing traces simplifying layout. In theexample of FIG. 2A, four Rx signals are routed on the top surface to Rxsensors 206, while the remaining four Rx signals can be routed on thebottom layer until required for connection to a Rx sensor 206.

The sensor device 115 may further comprise one or more transmit (Tx)sensors 210 that span across the bottom of the Rx sensor columns 205 asshown in FIG. 2A. Although illustrated in FIG. 2A with 2 Tx sensors 210Aand B for simplicity, the sensor device 115 may comprise one or more Txsensors 210 per sensor pattern 202 duplicate, as discussed in furtherdetail herein. As discussed in further detail herein, as the movingoptical target 110A moves across the measurement beam 105, each Rxchannel 207 may be configured to measure a mutual capacitance betweenits respective Rx sensors 206 (i.e., the Rx sensors it provides an Rxsignal to) and a corresponding Tx sensor(s) 210 (in the example of FIG.2A, Tx sensor 210A is the Tx sensor corresponding to the sensor pattern202).

Each Tx sensor 210 may emit large electric field lines that may attemptto couple to other components of the sensor device 115 (e.g., the firstobject they can ground to). It is important to minimize this when thetarget 110A is not present. Thus, sensor device 115 may comprise a guardchannel 217 coupled between the Rx sensor columns 205 and the Tx sensors210 to collapse those electric field lines before they reach the Rxcolumns 205. More specifically, the guard channel 217 may collapse theelectric field between the Rx sensor columns 205 and the Tx sensors 210in order to minimize direct capacitive coupling that may result when thetarget 110A is not present.

As the target 110A moves across the measurement beam 105, its preciselocation along the measurement beam 105 can be determined by the sensordevice 115 using mutual capacitive sensing, for example. The sensordevice 115 may comprise a processing device 212 and a memory 211, whichmay store instructions that the processing device 212 may execute toperform the embodiments discussed herein. The sensor device 115 may scanthe Rx sensors 206 of each Rx column 205. As used herein, a “scan” of anRx sensor (e.g., Rx sensor 206A) may refer to a Tx signal (e.g., a 5Vsquare waveform) being driven to the Tx sensor 210A (e.g., by a Txsignal generator—not shown) while a respective Rx channel 207 of the Rxsensor 206A drives its Rx signal (i.e., Rx signal 0) to the Rx sensor206A in order to measure the mutual capacitance between the Tx sensor210A and the Rx sensor 206A. As shown in FIG. 2A, when the target 110Ais located over Rx column 205C, it may capacitively couple the Tx sensor210A to the Rx sensors 206 in Rx column 205C. As the square wave Txsignal changes from low to high or high to low, if the sensor 206A andthe Tx sensor 210A are capacitively coupled, this may cause charge to bemoved on or off the Rx sensor 206A due to the capacitive coupling. Thus,when the sensor 206A and the Tx sensor 210A are coupled, the chargelevel of the Rx sensor 206A may move up and down based on the squarewave Tx signal. If the sensor 206A and the Tx sensor 210A are notcoupled, the charge level of the Rx sensor 206A does not move.

Sensor device 115 may further comprise a current source 213 that mayfunction to cancel out any changes in charge on the sensors 206. Thesensor device 115 may include a digital timer (not shown) which maymeasure the amount of time the current source 213 is required to beactive in order to cancel a change in charge on e.g., the Rx sensor206A. Thus, if Rx sensor 206A is not covered by the target 110A, it isnot capacitively coupled to the Tx sensor 210A and there is no change inthe charge of the Rx sensor 206A. In turn, the current source 213 is notactive (or, the amount of time it is active is 0), and the digital timermay output a signal corresponding to 0. If Rx sensor 206A is covered bythe target 110A, it is capacitively coupled to the Tx sensor 210A andthe charge of the Rx sensor 206A will change based on the square wave Txsignal. In turn, the current source 213 must move charge in and out ofthe Rx sensor 206A to maintain its balance and the digital timer maymeasure how long the current source 213 must remain active to performthis function. The digital timer may output a signal corresponding tothe time the current source 213 was active, and the sensor device 115may compare the time to a threshold. If the determined time exceeds thethreshold, the sensor device 115 may output a binary 1 for Rx signal 0(because Rx sensor 206A was driven by Rx signal 0).

For each RX sensor 206 scan, the time the current source 213 was on inorder to maintain the charge balance of that Rx sensor 206 is comparedto the threshold and a binary output for the Rx signal driving that Rxsensor 206 is generated. As discussed above, for a particular Rx sensor206, if the time the current source 213 is active during the scan isabove the threshold, then the output may be a binary 1, otherwise theoutput may be a binary 0. The sensor device 115 may utilize the binaryencoding of the output of the Rx sensors 206 from each Rx column 205 tocalculate and/or lookup the absolute position of the target 110A, asdiscussed in further detail herein. More specifically, each of theplurality of Rx columns 205 covers a distance (e.g., 2 mm) such thateach successive Rx column 205 indicates a position. The sensor device115 may determine an Rx column 205 whose Rx sensors 206 all have outputsof binary 1, and determine the position of the target 110A as theposition indicated by that Rx column 205. Modified threshold levels andadditional thresholds may be used for improved algorithms and increasedaccuracy.

It should be noted that in practical operation, there is always e.g.,interference present so the current source 213 may be active for aminimum amount of time during each scan to account for suchinterference. As a result, the threshold may correspond to a delta inthe total time the current source 213 is active that is large enough toaccount for such interference. For example, if Rx sensor 206A is notcovered by the target 110A, it is not currently capacitively coupled tothe Tx sensor 210A. However, the current source 213 would still beactive for relatively small amounts of time to account for the effectsof interference. Once Rx sensor 206A is covered by the target 110A andit is capacitively coupled to the Tx sensor 210A, then the amount oftime the current source 213 must be active may increase by orders ofmagnitude.

As shown in FIG. 2A, between consecutive Rx columns 205, only 1 out ofthe 4 Rx sensors 206 may be driven by a different Rx signal. Forexample, the 1st, 2nd, and 4th Rx sensors in Rx columns 205G and 205Hare all driven by signals 0, 1, and 7. However, the 3rd Rx sensor 206 incolumn 205G is driven by Rx signal 5 while the 3rd sensor 206 in Rxcolumn 205H is driven by Rx signal 6. This change from Rx column to Rxcolumn may be due to the use of gray code to ensure that there arealways 4 sensors active at a minimum when the target 110A is directlyover an Rx column 205.

To determine the position of the target 110A, the sensor device 115 mayinitially search for Rx columns 205 where the output of all 4 Rx sensors206 is a binary 1. However, the sensor device 115 may often timesdetermine that no Rx columns 205 meet this criteria, and in suchscenarios, it may proceed to search for Rx columns 205 where the outputof three of the Rx sensors 206 is a binary 1. Upon determining twoconsecutive Rx columns where the output of three of the Rx sensors 206is a binary 1, the sensor device 115 may determine that the target 110Ais between these two Rx columns and may perform additional postprocessing to look at the relative signal strength between the Rx sensorhaving the weakest output of each the two Rx columns to increase theresolution of the detected location of the target 110A throughinterpolation as discussed further with respect to FIG. 2B.

FIG. 2B illustrates a scenario when the target 110A is located betweentwo Rx columns 205J (including Rx sensors 206G-206J in rows 1-4respectively) and 205K (including Rx sensors 206K-206N in rows 1-4respectively). As shown in FIG. 2B, the target 110A is half way betweenthe Rx sensors 206 in rows 1, 2, 3, and 4 of Rx columns 205J and 205K.The Rx sensors 206 in rows 1, 2, and 4 of Rx columns 205J and 205K aredriven by the same Rx signal (0, 2, and 7 respectively). As a result,although the target 110A is split physically between Rx columns 205J and205K, because the Rx sensors 206 in rows 1, 2, and 4 of neighboring Rxcolumns 205J and 205K are driven by the same Rx signal (0, 2, and 7respectively), these Rx sensors 206 may be electrically shorted (i.e.they may appear electrically as if they were part of a single Rx columnand so the measured signal at these Rx sensors may be higher than thethreshold) and so a binary output of 1 will be read for Rx signals 0, 2,and 7 respectively (i.e., read at each of the Rx sensors 206 in rows 1,2, and 4 of Rx columns 205J and 205K). In row 3, where the target 110Ais split between Rx sensors 206I and 206M, the measured signal fromthose Rx sensors may be approximately half the measured signal from theother Rx sensors. This is because the Rx sensors 206 in row 3 of Rxcolumns 205J and 205K are driven by different Rx signals (5 and 6respectively) and so they are not electrically shorted (resulting in abinary output of 0 being read for Rx signals 5 and 6 respectively). As aresult, the sensor device 115 determines that the amount of time thecurrent source 213 must be active to keep Rx sensors 206I and 206Mbalanced is half the time required to keep the other Rx sensors 206 inRx columns 205J and 205K balanced.

FIG. 2C illustrates a diagram of the Rx signals 0-7 as the target 110Amoves, including the Rx signals read from the Rx sensors 206 when target110A is over Rx column 205C (i.e., Rx signals 0, 1, 3, and 4) as well asthe Rx signals read from each of the sensors 206G-206N when the target110A is located between Rx columns 205J and 205K (i.e., Rx signals 0, 2,5, 6, and 7). As can be seen, the Rx signals 5 and 6 have approximatelyhalf the peak as the Rx signals 0, 2, and 7 (read from electricallyconnected Rx sensors 206 in rows 1, 2, and 4 of Rx columns 205J and205K). Based on this, the sensor device 115 may determine that thetarget 110A is half way between Rx columns 205J and 205K (with aresolution of 1 mm on each Rx column 205J and 205K). Althoughillustrated with the target 110A half way between Rx columns 205J and205K, the sensor device 115 can interpolate to account for scenarioswhere the target 110A is closer to (covering more of) Rx column 205Jthan Rx column 205K and vice versa. In the above example, assuming thatthe measured signal of Rx sensor 206I was measured at 75% of themeasured signal from the other Rx sensors in Rx column 205J, and themeasured signal of Rx sensor 206M was measured at 25% of the measuredsignal from the other Rx sensors in Rx column 205K, the sensor device115 may determine that the target 110A is closer to Rx column 205J thanRx column 205K.

There may be scenarios where the target 110A is located 95% over column205J and 5% over column 205K. In these (and potentially other)scenarios, the sensor device 115 may still interpolate to give theposition based on the required accuracy. For example, if the desiredresolution is 2 mm accuracy, then the sensor device 115 may determinethat 95% is enough to generate the “1” value. However, if higherresolution is required, then the algorithm may be tuned to requireinterpolation based on the desired resolution.

Although illustrated with Rx sensor spacing of 2 mm over a 140 mm range,these measurements are for example purposes only, and the Rx sensorspacing can be any appropriate distance based on the desired resolution.The sensor device 115 may comprise the sensor pattern 202 of FIGS. 2Aand 2B repeated over any required intervals to cover the required e.g.,750 mm distance. To extend the 140 mm range in this example, the sensorpattern 202 may be duplicated with each duplicate coupled to a separateTx sensor 210. It should be noted that a new Tx sensor 210 may berequired for each duplicate of the Rx sensor pattern 202. This isbecause a 4-bit sensor pattern using 8 Rx signals (as illustrated inFIGS. 2A and 2B) results in 70 columns, as discussed above. Thus, a newTx sensor 210 is required every 70 columns otherwise the sensor device115 may be unable to distinguish which iteration of the sensor pattern202 the target is proximate to.

In this example, a total of 6 Tx sensors 210 would cover the full 750 mmrange. FIG. 2A illustrates a portion of a first duplicate sensor pattern202A (with 3 Rx columns of pattern 202A shown) which is coupled to a Txsensor 210B. In this scenario, 14 pins (8 Rx signals and 6 Tx signals)may be required to implement the sensor device 115. However, the numberof Rx and Tx signals may be optimized to ensure position detectionaccuracy. For example, 11 total Rx signals (n) spread over 5 Rx sensors(r) in each Rx column, and 1 Tx sensor, would also cover the full 750 mmlength with 2 mm accuracy using a total of 12 pins. FIG. 2D illustratesa table 250 that lists the maximum number of unique codes (Rx signalcombinations) using the combinatorial equation given above (totalcombinations=n!/(r!(n−r)!).

A PCB layout involving eight interweaved Rx signals that require lowparasitic and shielding from the six Tx signals as discussed in theabove embodiments may be complex to manufacture. An additional benefitof the above embodiments includes a simplified layout of a printedcircuit board (PCB) for the sensor device 115. As shown in FIGS. 2A and2B, all Rx signals run perpendicular to the Rx sensor columns 205 andare present on the surface of the sensor device 115 in an organized way,thus simplifying the layout. In addition, Tx signals can be separatedfrom the Rx signals and shielded under the currently active Tx sensor inthat region/pattern iteration.

In some embodiments, an Rx sensor pattern 202 may be coupled to multipleTx sensors 210. This may be useful in situations where e.g., a single Txsensor may become too large, resulting in a capacitive load that is toohigh for the I/O pin to drive efficiently (as the length of a Tx sensorincreases so does its area, which is directly proportional to itscapacitance). By utilizing multiple Tx sensors the sensor device 115 maydrive multiple Tx signals using individual pins for each.

The signal itself (time that current source 213 is on) is a highlysensitive analog signal that is based on balancing current sources, andcan change dramatically as a result. This varying capacitive baselinecan be tracked over time using the Rx sensors 206 that are not currentlycoupled to the target 110A. Because there is always at least one Rxcolumn 205 column covered by the target 110A, four of the eight Rxsignals always have a baseline value while the other four Rx signalsalways have an active value. The simplest baseline method is to averageall eight Rx signals and offset each Rx signal from this average. Theseoffsets are determined at manufacture and stored in the device. Furthertesting and refinement may allow elimination of this calibration step ifthe manufacturing variation is low. In an example where the target 110Ais between Rx columns and five Rx signals are active, the two Rx signalscorresponding to the ½ covered Rx sensors average out to the nominalcase of four Rx signals. The lack of a target can also be determined bycomparing Rx signal measurement with and without the Tx signal present.If no Rx signals are over the threshold and they are all close incalibrated value, then no target is present.

By ensuring that approximately half of the Rx sensors 206 are covered,while the other half are not, the baseline may be continuously updatedand changes in the average signal between them may be tracked. Withstandard capacitive sensing techniques this is not possible because Rxsignal increases can only be detected on the Rx sensor currently beingscanned. Stated differently, while an Rx sensor is being scanned, itsbaseline/threshold R signal value cannot be updated because there isnothing to compare it against i.e., there is no reference with which adelta change over time can be observed.

One concern with long distances and a metal framework (e.g., of themeasurement beam 105) is the signal to noise ratio. The sensor device115 may utilize a known metal target creating a uniform signal and theassumed ability to have a long scan period to filter out noise.Sufficient signal levels determine the maximum number of targets, and RXsensors, and sensor dimensions that can be accommodated with a singlesensor PCB. More specifically, as the sensor device 115 increases inarea the parasitic capacitance of the Rx and Tx sensors may increase,reducing the capacitive change when the target 110 is present over an Rxsensor 206. As the decrease in capacitive change signal approaches thesystem natural noise level, it becomes more difficult to determine ifthe signal at the Rx sensor 206 is above the threshold due to the target110A or due to noise. By averaging the signal over time it is possibleto differentiate the (generally) above threshold signal values caused bythe target 110A from the (generally) below threshold levels of randomnoise. Increasing the area of the Tx and Rx sensors increases the mutualcapacitance coupled between them. Increased capacitance results in ahigher signal when the target 110A is present assisting in avoidingfalse sensor threshold detections due to noise. The mechanicalconstraints of the system 100 may determine the area available for Rxsensors 206.

The embodiments described up to this point support a single target 110Abecause if two targets 110 are capacitively coupled to the same Tx andRx sensors, sensor device 115 cannot determine the position of eithertarget 110. FIG. 3A illustrates the sensor device 115 according to someembodiments of the present disclosure for detecting the position ofmultiple targets 110 along the measurement beam 105.

As can be seen, the Rx sensor patterns 202 and matching Tx sensors 210may be of short enough length that mechanically, two or more targets 110cannot occupy the same region/sensor pattern 202 of the sensor device115. Stated differently, the mechanical limits of the sensor device 115ensure that two targets 110 will never be coupled to the same TX sensor210. The sensor device 115 may use the Tx signals for each Tx sensor 210to differentiate the different targets 110. More specifically, eachtarget 110 may couple to a unique Tx sensor 210 out of the shared arrayof Tx sensors 210 and the sensor device 115 may enable each Tx sensor210 in sequence and determine the corresponding target 110's unique Rxsensor pattern. It should be noted that any target 110 may couple to anyTx sensor 210 because the passive metal coupling between the targets 110and the measurement beam 105 has the same orientation regardless. In theexample of FIG. 3A, each Rx sensor pattern 202 is five inches long,while each target 110 is ten inches.

FIG. 3B illustrates a sensor device 300 according to some embodiments ofthe present disclosure for detecting the position of multiple targets110 along the measurement beam 105. The sensor device 300 may comprisethe components of sensor device 115 and may further comprise a Tx sensor220 located on top of the Rx sensor pattern 202A. The Tx sensor 220 maybe coupled exclusively to a second target 110B while Tx sensor 210A maybe coupled exclusively to target 110A. Stated differently, each target110 must have a different/unique passive metal coupling orientation toallow coupling with only that target 110's corresponding Tx sensor. Inthis way, regardless of whether the targets 110A and 110B are locatedright next to each other (as shown in FIG. 3B) or far apart from eachother with respect to the Rx sensor pattern 202, the sensor device 300may still differentiate between them. The sensor device 300 may furthercomprise a second guard channel 217 that is coupled between the Rxsensor columns 205 and the Tx sensor 220 to collapse the electric fieldbetween the Rx sensor columns 205 and the Tx sensor 220 in order tominimize direct capacitive coupling that may result when the target 110Bis not present.

In operation, when the sensor device 115 is scanning Tx sensor 210A, itmay turn off Tx sensor 220, and when scanning Tx sensor 220, it may turnoff Tx sensor 210A. By enabling each target 110's dedicated TXsensor(s), the sensor device 300 can determine each target 110'sposition. Method 2 requires additional area to place the second Txsensor 220. This method can be extended similarly for more targets byadding unique Tx sensors and target orientations. FIG. 3C illustrates adiagram of the Rx signals 0-7 as the target 110A moves, including the Rxsignals read from each of the sensors 206G-206N (i.e., Rx signals 0, 2,5, 6, and 7) when the target 110A is located between Rx columns 205J and205K.

FIG. 4 is a flow diagram of a method 400 for detecting the position of atarget along a beam using capacitive sensing, in accordance with someembodiments of the present disclosure. Method 400 may be performed byprocessing logic that may comprise hardware (e.g., circuitry, dedicatedlogic, programmable logic, a processor, a processing device, a centralprocessing unit (CPU), a system-on-chip (SoC), etc.), software (e.g.,instructions running/executing on a processing device), firmware (e.g.,microcode), or a combination thereof. For example, the method 400 may beperformed by the sensor device 115 of FIGS. 2A, 2B, and 3A (as well asthe sensor device 300 of FIG. 3B) executing position detection firmware.

At block 405, the sensor device 115 may scan each of a plurality of Rxsensors 206, the plurality of Rx sensors organized into Rx columns 205and wherein the Rx sensors 206 of each Rx column 205 are driven by aunique combination of Rx signals from a set of Rx signals based on agray code.

At block 410, for each Rx sensor scan, the sensor device 115 may:compare a signal measured during the scan to a threshold and output abinary 1 if the measured signal is above the threshold and output abinary 0 if the measured signal is below the threshold.

At block 415, the sensor device 115 may determine the position of thetarget based on a binary encoding of the output of the Rx sensors 206from each Rx column 205, wherein each of the plurality of Rx columnscovers a distance such that each successive Rx column indicates aposition of the target 110A.

FIG. 5 illustrates an embodiment of a core architecture 500 of the PSoC®processing device, such as that used in the PSoC3® family of productsoffered by Cypress Semiconductor Corporation (San Jose, Calif.) withinwhich embodiments of the present disclosure may be implemented. In oneembodiment, the core architecture 500 includes a microcontroller 1102.The microcontroller 1102 includes a CPU (central processing unit) core1104 (which may correspond to processing device 130 of FIG. 1 ), flashprogram storage 1106, DOC (debug on chip) 1108, a prefetch buffer 1110,a private SRAM (static random access memory) 1112, and special functionsregisters 1114. In an embodiment, the DOC 1108, prefetch buffer 1110,private SRAM 1112, and special function registers 1114 are coupled tothe CPU core 1104 (e.g., CPU core 1006), while the flash program storage1106 is coupled to the prefetch buffer 1110.

The core architecture 500 may also include a CHub (core hub) 1116,including a bridge 1118 and a DMA controller 1120 that is coupled to themicrocontroller 1102 via bus 1122. The CHub 1116 may provide the primarydata and control interface between the microcontroller 1102 and itsperipherals (e.g., peripherals) and memory, and a programmable core1124. The DMA controller 1120 may be programmed to transfer data betweensystem elements without burdening the CPU core 1104. In variousembodiments, each of these subcomponents of the microcontroller 1102 andCHub 1116 may be different with each choice or type of CPU core 1104.The CHub 1116 may also be coupled to shared SRAM 1126 and an SPC (systemperformance controller) 1128. The private SRAM 1112 is independent ofthe shared SRAM 1126 that is accessed by the microcontroller 1102through the bridge 1118. The CPU core 1104 accesses the private SRAM1112 without going through the bridge 1118, thus allowing local registerand RAM accesses to occur simultaneously with DMA access to shared SRAM1126. Although labeled here as SRAM, these memory modules may be anysuitable type of a wide variety of (volatile or non-volatile) memory ordata storage modules in various other embodiments.

In various embodiments, the programmable core 1124 may include variouscombinations of subcomponents (not shown), including, but not limitedto, a digital logic array, digital peripherals, analog processingchannels, global routing analog peripherals, DMA controller(s), SRAM andother appropriate types of data storage, IO ports, and other suitabletypes of subcomponents. In one embodiment, the programmable core 1124includes a GPIO (general purpose IO) and EMIF (extended memoryinterface) block 1130 to provide a mechanism to extend the externaloff-chip access of the microcontroller 1102, a programmable digitalblock 1132, a programmable analog block 1134, and a special functionsblock 1136, each configured to implement one or more of the subcomponentfunctions. In various embodiments, the special functions block 1136 mayinclude dedicated (non-programmable) functional blocks and/or includeone or more interfaces to dedicated functional blocks, such as USB, acrystal oscillator drive, JTAG, and the like.

The programmable digital block 1132 may include a digital logic arrayincluding an array of digital logic blocks and associated routing. Inone embodiment, the digital block architecture is comprised of UDBs(universal digital blocks). For example, each UDB may include an ALUtogether with CPLD functionality.

In various embodiments, one or more UDBs of the programmable digitalblock 1132 may be configured to perform various digital functions,including, but not limited to, one or more of the following functions: abasic I2C slave; an I2C master; a SPI master or slave; a multi-wire(e.g., 3-wire) SPI master or slave (e.g., MISO/MOSI multiplexed on asingle pin); timers and counters (e.g., a pair of 8-bit timers orcounters, one 16 bit timer or counter, one 8-bit capture timer, or thelike); PWMs (e.g., a pair of 8-bit PWMs, one 16-bit PWM, one 8-bitdeadband PWM, or the like), a level sensitive I/O interrupt generator; aquadrature encoder, a UART (e.g., half-duplex); delay lines; and anyother suitable type of digital function or combination of digitalfunctions which can be implemented in a plurality of UDBs.

In other embodiments, additional functions may be implemented using agroup of two or more UDBs. Merely for purposes of illustration and notlimitation, the following functions can be implemented using multipleUDBs: an I2C slave that supports hardware address detection and theability to handle a complete transaction without CPU core (e.g., CPUcore 1104) intervention and to help prevent the force clock stretchingon any bit in the data stream; an I2C multi-master which may include aslave option in a single block; an arbitrary length PRS or CRC (up to 32bits); SDIO; SGPIO; a digital correlator (e.g., having up to 32 bitswith 4× over-sampling and supporting a configurable threshold); a LINbusinterface; a delta-sigma modulator (e.g., for class D audio DAC having adifferential output pair); an I2S (stereo); an LCD drive control (e.g.,UDBs may be used to implement timing control of the LCD drive blocks andprovide display RAM addressing); full-duplex UART (e.g., 7-, 8- or 9-bitwith 1 or 2 stop bits and parity, and RTS/CTS support), an IRDA(transmit or receive); capture timer (e.g., 16-bit or the like);deadband PWM (e.g., 16-bit or the like); an SMbus (including formattingof SMbus packets with CRC in software); a brushless motor drive (e.g.,to support 6/12 step commutation); auto BAUD rate detection andgeneration (e.g., automatically determine BAUD rate for standard ratesfrom 1200 to 115200 BAUD and after detection to generate required clockto generate BAUD rate); and any other suitable type of digital functionor combination of digital functions which can be implemented in aplurality of UDBs.

The programmable analog block 1134 may include analog resourcesincluding, but not limited to, comparators, mixers, PGAs (programmablegain amplifiers), TIAs (trans-impedance amplifiers), ADCs(analog-to-digital converters), DACs (digital-to-analog converters),voltage references, current sources, sample and hold circuits, and anyother suitable type of analog resources. The programmable analog block1134 may support various analog functions including, but not limited to,analog routing, LCD drive IO support, capacitance-sensing, voltagemeasurement, motor control, current to voltage conversion, voltage tofrequency conversion, differential amplification, light measurement,inductive position monitoring, filtering, voice coil driving, magneticcard reading, acoustic doppler measurement, echo-ranging, modemtransmission and receive encoding, or any other suitable type of analogfunction.

The embodiments described herein may be used in various designs ofmutual-capacitance sensing systems, in self-capacitance sensing systems,or combinations of both. In one embodiment, the capacitance sensingsystem detects multiple sense elements that are activated in the arrayand can analyze a signal pattern on the neighboring sense elements toseparate noise from actual signal. The embodiments described herein arenot tied to a particular capacitive sensing solution and can be used aswell with other sensing solutions, including optical sensing solutions,as would be appreciated by one of ordinary skill in the art having thebenefit of this disclosure.

In the above description, numerous details are set forth. It will beapparent, however, to one of ordinary skill in the art having thebenefit of this disclosure, that embodiments of the present disclosuremay be practiced without these specific details. In some instances,well-known structures and devices are shown in block diagram form,rather than in detail, in order to avoid obscuring the description.

Some portions of the detailed description are presented in terms ofalgorithms and symbolic representations of operations on data bitswithin a computer memory. These algorithmic descriptions andrepresentations are the means used by those skilled in the dataprocessing arts to most effectively convey the substance of their workto others skilled in the art. An algorithm is here and generally,conceived to be a self-consistent sequence of steps leading to a desiredresult. The steps are those requiring physical manipulations of physicalquantities. Usually, though not necessarily, these quantities take theform of electrical or magnetic signals capable of being stored,transferred, combined, compared and otherwise manipulated. It has provenconvenient at times, principally for reasons of common usage, to referto these signals as bits, values, elements, symbols, characters, terms,numbers, or the like.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise as apparent from the above discussion, itis appreciated that throughout the description, discussions utilizingterms such as “determining,” “detecting,” “comparing,” “resetting,”“adding,” “calculating,” or the like, refer to the actions and processesof a computing system, or similar electronic computing device, thatmanipulates and transforms data represented as physical (e.g.,electronic) quantities within the computing system's registers andmemories into other data similarly represented as physical quantitieswithin the computing system memories or registers or other suchinformation storage, transmission or display devices.

The words “example” or “exemplary” are used herein to mean serving as anexample, instance, or illustration. Any aspect or design describedherein as “example’ or “exemplary” is not necessarily to be construed aspreferred or advantageous over other aspects or designs. Rather, use ofthe words “example” or “exemplary” is intended to present concepts in aconcrete fashion. As used in this application, the term “or” is intendedto mean an inclusive “or” rather than an exclusive “or.” That is, unlessspecified otherwise, or clear from context, “X includes A or B” isintended to mean any of the natural inclusive permutations. That is, ifX includes A; X includes B; or X includes both A and B, then “X includesA or B” is satisfied under any of the foregoing instances. In addition,the articles “a” and “an” as used in this application and the appendedclaims should generally be construed to mean “one or more” unlessspecified otherwise or clear from context to be directed to a singularform. Moreover, use of the term “an embodiment” or “one embodiment” or“an implementation” or “one implementation” throughout is not intendedto mean the same embodiment or implementation unless described as such.

Embodiments descried herein may also relate to an apparatus forperforming the operations herein. This apparatus may be speciallyconstructed for the required purposes, or it may comprise ageneral-purpose computer selectively activated or reconfigured by acomputer program stored in the computer. Such a computer program may bestored in a non-transitory computer-readable storage medium, such as,but not limited to, any type of disk including floppy disks, opticaldisks, CD-ROMs and magnetic-optical disks, read-only memories (ROMs),random access memories (RAMs), EPROMs, EEPROMs, magnetic or opticalcards, flash memory, or any type of media suitable for storingelectronic instructions. The term “computer-readable storage medium”should be taken to include a single medium or multiple media (e.g., acentralized or distributed database and/or associated caches andservers) that store one or more sets of instructions. The term“computer-readable medium” shall also be taken to include any mediumthat is capable of storing, encoding, or carrying a set of instructionsfor execution by the machine and that causes the machine to perform anyone or more of the methodologies of the present embodiments. The term“computer-readable storage medium” shall accordingly be taken toinclude, but not be limited to, solid-state memories, optical media,magnetic media, any medium that is capable of storing a set ofinstructions for execution by the machine and that causes the machine toperform any one or more of the methodologies of the present embodiments.

The algorithms and displays presented herein are not inherently relatedto any particular computer or other apparatus. Various general-purposesystems may be used with programs in accordance with the teachingsherein, or it may prove convenient to construct a more specializedapparatus to perform the required method steps. The required structurefor a variety of these systems will appear from the description below.In addition, the present embodiments are not described with reference toany particular programming language. It will be appreciated that avariety of programming languages may be used to implement the teachingsof the embodiments as described herein.

The above description sets forth numerous specific details such asexamples of specific systems, components, methods, and so forth, inorder to provide a good understanding of several embodiments of thepresent disclosure. It will be apparent to one skilled in the art,however, that at least some embodiments of the present disclosure may bepracticed without these specific details. In other instances, well-knowncomponents or methods are not described in detail or are presented insimple block diagram format in order to avoid unnecessarily obscuringthe present embodiments. Thus, the specific details set forth above aremerely exemplary. Particular implementations may vary from theseexemplary details and still be contemplated to be within the scope ofthe present embodiments.

It is to be understood that the above description is intended to beillustrative and not restrictive. Many other embodiments will beapparent to those of skill in the art upon reading and understanding theabove description. The scope of the embodiments should, therefore, bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

What is claimed is:
 1. An apparatus comprising: a plurality of receive(Rx) sensors organized into a plurality of Rx columns, each Rx sensor ofthe plurality of Rx sensors driven by an Rx signal of a set of Rxsignals; a transmit (Tx) sensor, the Tx sensor configured to couple toRx sensors of one or more Rx columns in response to a target moving intoproximity of the one or more Rx columns; a processing device operativelycoupled to the memory, the processing device configured to: scan each ofthe plurality of Rx sensors; and determine a position of the targetbased on the scan of each of the plurality of Rx sensors using mutualcapacitive sensing; and a guard channel coupled between the plurality ofRx columns and the Tx sensor to collapse electric field lines generatedby the Tx sensor when the target is not present.
 2. The apparatus ofclaim 1, wherein the Rx sensors of each Rx column are driven by a uniquecombination of Rx signals of the set of Rx signals based on a gray code.3. The apparatus of claim 1, wherein to determine the position of thetarget, the processing device is configured to: for each Rx sensor scan:compare a signal measured during the scan to a threshold; and output abinary 1 if the measured signal is above the threshold and output abinary 0 if the measured signal is below the threshold; and determinethe position of the target based on a binary encoding of the output ofthe Rx sensors from each Rx column, wherein each of the plurality of Rxcolumns covers a distance such that each successive Rx column indicatesa position.
 4. The apparatus of claim 3, wherein to determine theposition of the target based on the binary encoding of the output of theRx sensors from each Rx column, the processing device is furtherconfigured to: determine an Rx column of the plurality of Rx columnswhose corresponding Rx sensors each have an output of binary 1; anddetermine as the position of the target, a position indicated by the Rxcolumn whose corresponding Rx sensors each have an output of binary 1.5. The apparatus of claim 3, further comprising: a current sourceconfigured to maintain a current balance of each of the plurality of RXsensors, and wherein the measured signal of an RX sensor scancorresponds to an amount of time the current source is active tomaintain a current balance of the Rx sensor being scanned.
 6. Theapparatus of claim 1, further comprising: a second plurality of Rxsensors organized into a second plurality of Rx columns; a Tx sensorconfigured to couple to Rx sensors of one or more of the secondplurality of Rx columns in response to a second target moving intoproximity of the one or more second Rx columns.
 7. The apparatus ofclaim 6, wherein the processing device is further configured to: scaneach of the second plurality of Rx sensors; and determine a position ofthe second target based on the scan of each of the second plurality ofRx sensors using mutual capacitive sensing.
 8. The apparatus of claim 1,wherein the Tx sensor is turned off when being scanned.
 9. The apparatusof claim 1, wherein the plurality of Rx columns comprises an Rx sensorpattern.
 10. The apparatus of claim 9, further comprising: one or moreadditional Rx sensor patterns and one or more additional Tx sensors. 11.A system comprising: a measurement beam; one or more targets configuredto move along the measurement beam; and a sensor device located withinthe measurement beam, the sensor device comprising: a plurality ofreceive (Rx) sensors organized into a plurality of Rx columns, each Rxsensor of the plurality of Rx sensors driven by an Rx signal of a set ofRx signals; a transmit (Tx) sensor, the Tx sensor configured to coupleto Rx sensors of one or more Rx columns in response to a target of theone or more targets moving into proximity of the one or more Rx columns;a processing device configured to: scan each of the plurality of Rxsensors; and determine a position of the target based on the scan ofeach of the plurality of Rx sensors using mutual capacitive sensing; anda guard channel coupled between the plurality of Rx columns and the Txsensor to collapse electric field lines generated by the Tx sensor whenthe target is not present.
 12. The system of claim 11, wherein the Rxsensors of each Rx column are driven by a unique combination of Rxsignals of the set of Rx signals based on a gray code.
 13. The system ofclaim 11, wherein to determine the position of the target, theprocessing device is configured to: for each Rx sensor scan: compare asignal measured during the scan to a threshold; and output a binary 1 ifthe measured signal is above the threshold and output a binary 0 if themeasured signal is below the threshold; and determine the position ofthe target based on a binary encoding of the output of the Rx sensorsfrom each Rx column, wherein each of the plurality of Rx columns coversa distance such that each successive Rx column indicates a position. 14.The system of claim 13, wherein to determine the position of the targetbased on the binary encoding of the output of the Rx sensors from eachRx column, the processing device is further configured to: determine anRx column of the plurality of Rx columns whose corresponding Rx sensorseach have an output of binary 1; and determine as the position of thetarget, a position indicated by the Rx column whose corresponding Rxsensors each have an output of binary
 1. 15. The system of claim 13,wherein the sensor device further comprises: a current source configuredto maintain a current balance of each of the plurality of RX sensors,and wherein the measured signal of an RX sensor scan corresponds to anamount of time the current source is active to maintain a currentbalance of the Rx sensor being scanned.
 16. The system of claim 11,wherein the sensor device further comprises: a second plurality of Rxsensors organized into a second plurality of Rx columns; a Tx sensorconfigured to couple to Rx sensors of one or more of the secondplurality of Rx columns in response to a second target of the one ormore targets moving into proximity of the one or more second Rx columns.17. The system of claim 16, wherein the processing device is furtherconfigured to: scan each of the second plurality of Rx sensors; anddetermine a position of the second target based on the scan of each ofthe second plurality of Rx sensors using mutual capacitive sensing. 18.The system of claim 11, wherein the Tx sensor is turned off when beingscanned.
 19. The system of claim 11, wherein the plurality of Rx columnscomprises an Rx sensor pattern.
 20. The system of claim 19, wherein thesensor device further comprises: one or more additional Rx sensorpatterns and one or more additional Tx sensors.